In the case of the static subjects the personality factors like ability to work hard, ability to understand the things, one's memory power, quality of one's peer group, quality of the guidance one can get etc comes into play.
One has to remember that everything that is taught in the coaching centers of static subjects is readily available in the text books. If the text books are not sufficient, notes of the coaching centers is readily available in the market.
One has to also remember that in coaching centers everything is taught superficially. This shallow knowledge is unhelpful in answering the questions in the exam which are being asked now a days. This is particularly true in case of subjects with huge syllabus like History, Geography etc. So after listening to the lecture, one has to study the textbooks to get a deep picture of the things. Coaching in this case only familiarizes the subject to the beginners. So what is the use of coaching then?
If one is patient enough and works hard, the necessity of the coaching centers can be eliminated. But if one has a starting problem in reading an entirely unfamiliar subject, he may join the coaching center for that static subject.
Some persons may remember the things by just reading the topics of the subject a few times. But to many persons listening to some topics is sometimes helps them more in memorizing the things than just reading them. Here coaching definitely helps. As the coaching centers only teaches superficially, this advantage of coaching is some what neutralized. But I have to admit that the basic structure of the subject sticks in the mind.
Some subjects require proper understanding of the subject unlike some subjects which require lesser understanding and more memory power. Philosophy comes under former category, History comes under later category. Obviously in this case coaching actually helps. Literature subjects like Pali too require coaching which makes life easy.
In my opinion, if there is someone who can guide you well, tell you what to read and where to read them from, clarify your doubts, then there is absolutely no need of any coaching for any subject. I will elaborate on this now.
Even in coaching centers, many times they tell the students to read from their notes and not from any textbooks. It is suicidal to follow this as their notes are ill-organised and written badly in most of the cases, not comprehensive in all the cases. Reading only their notes wont help you in answering most of the questions which are asked now a days. Reading from textbooks is must. Now, there may many textbooks for a subject, and not every thing is given at one place in a text book. Also, not everything given in the textbooks is useful. If there is someone to guide and tell you what to read and where to read from, your time wont be wasted. Coaching centers definitely don't do this.
If there is a quality peer group, your work is simplified, as through discussion your understanding improves. Shelf-life of the subject, in the mind improves. Coaching center's need will be reduced.
So I would say, analyse the subject and your personality from the above mentioned angles and assess the need of coaching yourself.